Field of the Invention
This disclosure is related to the field of polymer interlayers for multiple layer panels and multiple layer panels having at least one polymer interlayer sheet. Specifically, this disclosure is related to the field of polymer interlayers comprising a compatibilizer.
Description of Related Art
Multiple layer panels are generally panels comprised of two sheets of a substrate (such as, but not limited to, glass, polyester, polyacrylate, or polycarbonate) with one or more polymer interlayers sandwiched there between. The laminated multiple layer glass panels are commonly utilized in architectural window applications and in the windows of motor vehicles and airplanes, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. The main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, to keep the layers of glass bonded even when the force is applied and the glass is broken, and to prevent the glass from breaking up into sharp pieces. Additionally, the interlayer may also give the glass a much higher sound insulation rating, reduces UV and/or IR light transmission, and enhances the aesthetic appeal of the associated window. In regard to the photovoltaic applications, the main function of the interlayer is to encapsulate the photovoltaic solar panels which are used to generate and supply electricity in commercial and residential applications.
In order to achieve the desired and optimal sound insulation for the glass panel, it has become common practice to utilize multilayered interlayers with at least one soft “core” layer sandwiched between two more rigid “skin” layers. Theses layers of the interlayer are generally produced by mixing a polymer resin such as poly(vinyl butyral) with one or more plasticizers and melt processing the mix into a sheet by any applicable process or method known to one of skill in the art, including, but not limited to, extrusion, with the layers being combined by processes such as co-extrusion and lamination. Other additional ingredients may optionally be added for various other purposes. After the interlayer sheet is formed, it is typically collected and rolled for transportation and storage and for later use in the multiple layer glass panel, as discussed below.
Contemplated polymer interlayers include, but are not limited to, polyvinyl acetals (PVA) (such as poly(vinyl butyral) (PVB) or poly(vinyl isobutyral), an isomer of poly(vinyl butyral) (which may be referred as PViB or PVisoB), polyurethane (PU), poly(ethylene-co-vinyl acetate) (EVA), polyvinylchloride (PVC), polyethylenes, polyolefins, ethylene acrylate ester copolymers, poly(ethylene-co-butyl acrylate), copolyesters, silicone elastomers, epoxy resins, and any acid copolymers such as an ethylene/carboxylic acid copolymer and its ionomers, derived from any of the foregoing possible thermoplastic resins. PVB and its isomer polyvinyl isobutyral, polyvinyl chloride, ionomers, and polyurethane are preferred polymers generally for interlayers.
Multilayer laminates can include multiple layer glass panels and multilayer polymer films. In certain embodiments, the multiple polymer films in the multilayer laminates may be laminated together to provide a multilayer film or interlayer. In certain embodiments, these polymer films may have coatings, such as metal, silicone or other applicable coatings known to those of ordinary skill in the art. The individual polymer films which comprise the multilayer polymer films may be laminated together using an adhesive as known to those of ordinary skill in the art.
The interlayer may be a single layer, a combination of more than one single layer, a multilayer that has been coextruded, multiple layers laminated together to form a multilayer interlayer, a combination of at least one single layer and at least one multilayer, or a combination of multilayer sheets.
The following offers a simplified description of the manner in which multiple layer glass panels are generally produced in combination with the interlayers. First, at least one polymer interlayer sheet (single or multilayer) is placed between two substrates and any excess interlayer is trimmed from the edges, creating an assembly. It is not uncommon for multiple polymer interlayer sheets or a polymer interlayer sheet with multiple layers (or a combination of both) to be placed within the two substrates creating a multiple layer glass panel with multiple polymer interlayers. Then, air is removed from the assembly by an applicable process or method known to one of skill in the art; e.g., through nip rollers, vacuum bag or another deairing mechanism. Additionally, the interlayer is partially press-bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding is rendered more permanent by a high temperature and pressure lamination process, or any other method known to one of ordinary skill in the art such as, but not limited to, autoclaving.
Often, polymer interlayers that do not meet all of the desired properties (for example, off grade material that does not meet at least one property specification) or polymer interlayer trim, (both referred to hereinafter as “recycle” or “recycled” material) may be recycled during the production process, such as during the extrusion process. The recycled material may be fed directly back into the extruder or mixer, or it may be further processed, such as chopped into small pieces or processed into pellets or other shapes, and then mixed with the resin(s) and plasticizer (and any other additives) prior to the extruder or other mixing device. Depending on the particular quality problem (such as contamination, moisture level, color, and the like), different levels of recycled material may be used. For example, if the recycled material has a high level of haze, lower levels may be incorporated into the mixture so that the recycled material does not increase the haze level in the final product, or if the recycled material includes multiple resin types and/or multiple plasticizers, the recycled material may be incompatible with the particular product being produced. For example, PVB formulations containing non-standard plasticizer and/or PVB resin having different residual hydroxyl levels will not be compatible with the standard formulations.
Poly(vinyl butyral) (PVB) is a copolymer containing vinyl acetate, vinyl alcohol and vinyl butyral components. The vinyl acetate component is the result of residual groups remaining after the hydrolysis of poly(vinyl acetate) to form poly(vinyl alcohol). The poly(vinyl alcohol) is then used in the process. The vinyl alcohol component is the result of residual groups remaining after acetalizing the poly(vinyl alcohol) with butyraldehyde to form poly(vinyl butyral). The content of residual vinyl acetate components in commercial grade PVB is generally in the range of about 1 to 15 wt. %, more commonly less than 4 wt. %. In the past, standard commercial grade PVB for multiple layer glass panels generally had a residual vinyl alcohol (also referred to as residual hydroxyl) content (% PVOH) of about 18 to 21 wt. %, more commonly about 18 to 19.5 wt. %. More recently, development of multilayer polymer interlayers for laminated glass has introduced different and more complicated product configurations, especially in polymer interlayers used to help improve acoustic properties (noise reduction) of the polymer interlayer and the final multiple layer glass panel. Multiple layer polymer interlayers are often produced from multiple different resins each having a different residual vinyl alcohol and/or residual vinyl acetate level. These multiple layer polymer interlayers have been developed to provide improved acoustical performance while retaining many of the other standard safety glass performance functions. In such multiple layer polymer interlayers used to improve acoustic performance (among other improvements), the resin used in the core (or inner) layer often has very low residual vinyl alcohol content, such as % PVOH of about 10 to 11 wt. %, while the resin used in the skin (outer) layer(s) may have a residual vinyl alcohol content (% PVOH) of about 18 to 19.5 wt. %. Other variations, different numbers of resins, or resins having different levels of residual vinyl alcohol content may also be used. Additionally, the multilayer interlayer may have different configurations of resins in the individual layers as desired, such as, for example a core layer resin having a higher % PVOH (such as 19.5 to 30 wt. %) than the skin layer (having lower residual vinyl alcohol content, such as % PVOH of about 10 to 19.5 wt. %).
One of the problems in the manufacture of polymer interlayers using certain types, or mixtures of certain types, of resins or recycled interlayer sheet comprising different resin and/or plasticizer types is haze or poor optical clarity. Haze is caused by a number of different factors, but one cause is the difference in levels of residual hydroxyl content in the resins used to produce the polymer interlayers. Different types of resins are used to produce polymer interlayers with different performance properties, such as adhesion, impact resistance, acoustic properties, mechanical properties, as well as other properties. The different resin types may have different levels of residual hydroxyl content, residual vinyl acetate content, or even different aldehydes if they were acetalized with different aldehyde groups. These different resins may also have different refractive indices.
The refractive index of a substance, such as an interlayer, is the measure of the speed of light through the substance with respect to the speed of light in vacuum. If there is a difference between the refractive index of the layers of a multiple layer interlayer, for example, because different resins are being used in the individual layers, then when the multilayer interlayer is recycled (melt mixing back into the polymer interlayer), the resulting polymer interlayer will often have high haze due to incompatibility between different resins.
Clarity of the interlayer, and more importantly, the glazing or multiple layer panel, is one of the critical quality parameters. Clarity is determined by measuring the level of haze in the multiple layer panel, as further described below. The level of haze must be very low so that the multiple layer panel is clear (and often transparent). In addition to haze, there are other optical quality defects, such as visible optical defects in the interlayer, that cause light scattering and make the defect visible to the eye that may cause optical distortion in the glass panel as well. Both haze and other visible optical defects are caused by light scattering due to the blending or mixing different polymers or plasticizer together, or the contamination from such different polymers and/or plasticizer where there is a sufficiently large difference in the refractive index between the different polymers or plasticizers, or the matrix and the contaminants.
The presence of haze or other optical quality defects in the final unitary structure of a multilayer laminate glass panel can be problematic because a certain degree of optical quality is necessary in many (if not most) of the end-use commercial applications of multilayer laminate glass panels (e.g., vehicular, aeronautical and architectural applications). Thus, the creation of multilayer laminate glass panels with commercially acceptable levels of low haze and good clarity is paramount in the art of multiple layer glass panel manufacturing. Because of the different properties and types of resins used to produce multiple layer polymer interlayers, such as a trilayer polymer interlayer having a soft core layer and harder skin layers, the multiple layer polymer interlayers, are difficult to reuse or recycle in large quantities. Only small amounts or percentages of the multiple layer polymer interlayers have been successfully used in the past. Additionally, it is often hard to reuse or recycle large quantities of unknown or varying recycle materials for the same reasons because the materials may be incompatible.
Other methods for recycling multilayer materials having different resin types have also been tried. For example, attempts to separate the resin and plasticizer by extraction of the plasticizer and recovery of the resin has been tried, but the process is not cost effective and is very resource intensive. The recycle materials could be used for other applications where haze and/or clarity are not a concern, but most times this approach is not economical because the PVB interlayer would then be sold at a lower value and would lose too much of its original value.
Summarized, optical quality defects such as haze and other visible optical defects are common problems in the field of multiple layer glass panels, particularly those used in applications which require higher levels of optical or visual quality. It is now common to use a multilayer interlayer in order to provide high performance laminates having specialized properties, such as improved acoustics. The use of multilayer interlayers, however, very often results in difficulties when attempting to recycle the multilayer materials because only a small amount of the recycle material could be recycled due to optical problems, such as haze and/or other optical quality defects. As a result, large quantities of recycle materials have to be disposed of in other ways, such as sale at reduced value or by landfilling, with little or no value (and potentially an added cost). Accordingly, there is a need in the art for improving the recyclability of multiple layer polymer interlayer without a reduction in optical, mechanical, and acoustic characteristics of a polymer interlayer, and a need for the development of process to recycle multiple layer polymer interlayer.